avcodec/cbs_av1: fix setting FrameWidth in frame_size_with_refs()

Section 5.9.7 of the spec states

    UpscaledWidth = RefUpscaledWidth[ ref_frame_idx[ i ] ]
    FrameWidth    = UpscaledWidth
    FrameHeight   = RefFrameHeight[ ref_frame_idx[ i ] ]
    RenderWidth   = RefRenderWidth[ ref_frame_idx[ i ] ]
    RenderHeight  = RefRenderHeight[ ref_frame_idx[ i ] ]

Meaning FrameWidth must not be set to RefFrameWidth[ ref_frame_idx[ i ] ]
like we're currently doing.

Reviewed-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>
Signed-off-by: James Almer <jamrial@gmail.com>

libavcodec/cbs_av1_syntax_template.c

@@ -553,7 +553,7 @@ static int FUNC(frame_size_with_refs)(CodedBitstreamContext *ctx, RWContext *rw,
             infer(render_height_minus_1, ref->render_height - 1);
 
             priv->upscaled_width = ref->upscaled_width;
-            priv->frame_width    = ref->frame_width;
+            priv->frame_width    = priv->upscaled_width;
             priv->frame_height   = ref->frame_height;
             priv->render_width   = ref->render_width;
             priv->render_height  = ref->render_height;